signalAll in Condition interface vs notifyAll in object
http://stackoverflow.com/questions/10407708/signalall-in-condition-interface-vs-notifyall-in-object
条件Condition中的signalALL 和 Object中的 notifyALL有啥区别?
Java中重写equals方法
public boolean equals(Objects x){
if(this == x) return true;
if(x == null) return false;
if(this.getClass() != x.getClass()) return false;
Date that = (Date) x;
if(this.day != that.day) return false;
return true;
}